DESCRIPTION (Verbatim from Applicant's Abstract): Transferrin-binding proteins A and B (TbpA and TbpB) are components of a surface-exposed, human transferrin receptor that is expressed by Neisseria gonorrhoeae. Because these proteins are well conserved and not subject to phage or antigenic variation, they have been focused on as potential vaccine candidates. The overall goal of this proposal is to determine how all of the components of the gonococcal transferrin receptor complex work and if both characterized components are immunogenic. The specific aims of the proposal address the following questions: 1. How are all of the components of the transferrin-receptor complex organized in the gonococcal outer membrane to facilitate transferrin interaction and transferrin-iron acquisition? Determining the topology and stoichiometry of this receptor is critical for our understanding of what regions are required for function and what domains are accessible to the immune system. Deletion, insertion and site-specific mutagenesis will be performed on TbpA and TbpB to establish structure/function relationships in the characterized components of the receptor. 2. What is the molecular mechanism that coordinately regulates the expression of tbpA and tbpB? Identifying the promoter and other regulatory regions that effect tbpA and tbpB expression will lead to a better understanding of how optimal levels of Tbp proteins are achieved and maintained. 3. Do the components of the transferrin-receptor generate an immune response, and if so, what are the biological activities of Tbp-specific antibodies? Mucosal secretion and serum samples of N. gonorrhoeae-infected men and women will be screened for the presence and type of antibodies against the components of the transferrin receptor. With any antibodies we detect, we will conduct functional assays including transferrin blocking, complement-mediated killing and phagocytic killing assays. We will also immunize rabbits with all or parts of the transferrin receptor to determine whether functional antibodies can be elicited.